Effect of Soil Thermal Heterogeneity on Permafrost Evolution

摘要

The hydrology and carbon balance of cold regions are drastically influenced by the presence of permafrost in the subsurface. There is little work in the literature attending to the impact of heterogeneities upon the long-term and short-term evolution of permafrost bodies. This local heterogeneity, however, may be a major driver in talik formation which, in turn, can impact landscape evolution, hydrologic connectivity, and greenhouse gas emission. In this research, a freeze-thaw code based on the non-isothermal phase transition criterion (enthalpy-based) is used for studying the effect of heterogeneity on the soil-water-ice system-'s thermal processes. A trust region algorithm is implemented for solving the highly non-linear system of equations. The results of the developed tool are successfully verified against the existing analytical solution for a three-zone one-dimensional medium presented by Lunardini (1985). Using the FEM-based tool developed in this research, two-dimensional freeze/thaw simulations are run in ensembles of spatially correlated heterogeneous soils with spatially heterogeneous freezing points in order to better elucidate the relative impact of various forms of heterogeneity on local permafrost table evolution. The results of the simulations of a domain with stochastically distributed thermal properties illustrate that local heterogeneity has conditional influence on the long-term permafrost body evolution and talik formations.